This content originally appeared on DEV Community and was authored by Danish Saleem
In this chapter we cover the 3 main primitive type conversions: to string, to number and to Boolean.
Make sure you check back for the next chapter which will be all about basic operators!
Converting Types
Most of the time, operators and functions in JavaScript automatically values into to the right types. For example, mathematical operators will convert values to number in order to perform calculations.
However, sometimes you need to explicitly convert values to number to a specific type. In this chapter we will cover some primitive type conversions.
String Conversion
There are a few ways to convert a value to a string but the most straight forward is by using the String() function. Some build in JavaScript functions such as alert() will always convert the value to a string in order to display it.
Examples:
let numToString = String(1); // Output: "1"
let trueToString = String(true); // Output: "true"
let falseToString = String(false); // Output: "fale"
let nullToString = String(null); // Output: "null"
let undefinedToString = String(undefined); // Output: "undefined"
let arrayToString = String([1, 2, 3]); // Output: "1, 2, 3"
Numeric Conversion
Numeric conversions are the useful when the value is read from a string-based source where a number is expected. Mathematical functions and expressions will automatically convert string values into numbers, but it can also be achieved using the Number() function.
Examples:
let stringToNumber = Number("123"); // Output: 123
let wordToNumber = Number("Hello"); // Output: NaN
let calcToNumber = "10" / "2"; // Output: 5
let trueToNumber = Number(true); // Output: 1
let falseToNumber = Number(false); // Output: 0
let nullToNumber = Number(null); // Output: 0
let undefinedToNumber = Number(undefined); // Output: NaN
let emptyStringToNumber = Number(""); // Output: 0
Boolean Conversion
Boolean conversions are quite simple and happen mostly in logical operations but can also be done by using the Boolean() function. Values that are considered empty (such as 0, null, NaN, undefined and empty strings) become false and other values become true.
Double exclamation marks can also be used as a shorthand Boolean conversion.
Examples:
let stringToBoolean = Boolean("Hello"); // Output: true
let stringFalseToBoolean = Boolean("false"); // Output: false
let emptyStringToBoolean = Boolean(""); // Output: false
let numberToBoolean = Boolean(123); // Output: true
let nullToBoolean = Boolean(null); // Output: false
let zeroToBoolean = Boolean(0); //output: false
let oneToBoolean = Boolean(1); // Output: true
// Shorthand Conversion
let value = "Hello";
console.log(!!value); // Output: true
Summary
- The most widely used conversions are to
string, tonumberand toBoolean. -
Stringconversion occurs when we output something and is usually obvious. -
Numericconversion occurs in mathematical operations. - Boolean conversion occurs in logical operations.
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This content originally appeared on DEV Community and was authored by Danish Saleem
Danish Saleem | Sciencx (2021-12-06T10:03:14+00:00) JavaScript for Beginners – Chapter 3: Type Conversions. Retrieved from https://www.scien.cx/2021/12/06/javascript-for-beginners-chapter-3-type-conversions/
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